1. Field of the Invention
The present invention relates to a knee bolster structure which is mounted onto an instrument panel provided in a vehicle in order to buffer a shock transmitted to the thigh portion of an occupant from the knee thereof in a vehicle collision or the like.
2. Related art
For example, when a vehicle collision occurs, since an occupant wears a seat belt, the upper body of the occupant is restricted toward the seat side of the vehicle. However, the knees of the occupant are caused to project forwardly to strike against the instrument panel side of the vehicle, so that the thigh portions of the occupant are heavily damaged through the knees. Conventionally, there is provided a knee bolster which is used to absorb or buffer the shocks given to the thigh portions of the occupant due to the secondary collision of the occupant in a vehicle collision. Here, as energy absorbing means such as a knee bolster, such means is assumed to be efficient that can be displaced while maintaining a given level of deceleration, that is, a given level of drag in a displaceable range. In view of this, the conventional knee bolster is also devised elaborately so that it is able to perform the above-mentioned function.
In FIG. 10, there is shown a conventional knee bolster which is generally used. The present knee bolster 1a comprises a panel 2 for closing an opening 16 formed in an instrument panel 13, and two stays 3a each of which has one end side to be fixed to the panel 2 with the other end side to be fixed to a reinforcement (not shown).
The stay 3a, as shown in FIGS. 10 and 11, includes a bottom surface 6 and two wall portions 7 respectively rising up from the two sides of the bottom surface 6, while the stay 3a has an upwardly facing U-shaped section. Also, as shown in FIG. 12, a notch 8 is formed substantially in the central portion of each of the wall portions 7. The notch 8 is used to stabilize the deformation of the stay 3a in an vehicle collision or the like and, due to formation of the notch 8, in a vehicle collision or the like, the stay 3a can begin to deform around the notch 8 formation portion. This allows the knee bolster 1a to make a constant displacement regardless of the operation direction of a collision force. By the way, instead of the notch 8, there may be opened up a hole in the notch 8 formation portion.
Conventionally, there are known many techniques which relate to the knee bolster. For example, some of them are disclosed in Japanese Patent Publication No. 2-175455 of Heisei, Japanese Patent Publication No. 7-267026 of Heisei, Japanese Patent Publication No. 7-81508 of Heisei, and the like. In particular, in Japanese Patent Publication No. 2-175455 of Heisei, there is disclosed a knee protector structure for a vehicle which comprises a protector main body (which corresponds to the above-mentioned panel) (5) and a knee protector upper (which corresponds to the above-mentioned stay) (3); while, the knee protector upper (3) includes bending portions (13) bendable due to a shock load acting on the protector main body (5), and a bent member (17) bridging over the bending portions (13) and having two end portions respectively fixed to the knee protector upper (3).
Also, in Japanese Patent Publication No. 7-267026 of Heisei, there is disclosed a knee protector structure for a vehicle which comprises a pair of substantially V-shaped brackets (which correspond to the above-mentioned stay) (11) each having a bending line (11a) in the bottom portion thereof, and a knee protector main body (which corresponds to the above-mentioned panel) (12) which is disposed in the rear of the bending lines (11a) between the pair of brackets (11), (11); and, each of the brackets (11) includes a recessed portion or a projecting portion which extends along the longitudinal direction thereof. The recessed portion or projecting portion is formed such that the level difference amount thereof is larger in the front portion of the bending line (11a) than in the rear portion of the bending line (11a) and increases gradually from the bending line (11a) toward the front end portion thereof. Also, on the bracket (11), there is mounted a substantially V-shaped upper bracket (18) including a bending line (18a) which is so formed as to bridge over the above-mentioned bending line (11a). That is, according to the present knee protector structure, the brackets are bent around the bending lines (11a) and (18a) to thereby absorb the shock energy stably and, at the same time, the level difference amount of the recessed portion or projecting portion is so set as to increase gradually toward the front end portion thereof to thereby prevent the knee protector from being vibrated in a vehicle collision or the like.
Further, in Japanese Patent Publication No. 7-81508 of Heisei, there is disclosed a knee protector for a car which comprises a first member (11), which is bent formed into a substantially V-like shape having the front end side thereof fixed to a steering member (2) and has a substantially U-shaped transverse section, and a second member (12) which is fixed at the two front and rear portions thereof to the first member (11) and is disposed on the upper side of the first member (11); and, the second member (12) has a shape which can be fitted into the first member (11) in a car collision or the like. That is, the present knee protector for a car is characterized in that the fitting of the second member (12) into the first member (11) facilitates and stabilizes the deformation of the knee protector to thereby prevent a crushing stroke from being interfered in a car collision or the like.
In the case of the conventional knee bolster 1a shown in FIGS. 10 to 12, as shown in FIG. 13, in a vehicle collision or the like, the panel 2 is pushed by the knee 15 of the occupant and is bent starting from the notch 8 portion thereof to thereby be able to stabilize the mode of deformation thereof; but, when the deformation starts, stresses are concentrated onto the notch 8 portion thereof to thereby reduce the drag of the bolster 1a. That is, in the conventional knee bolster 1a, there arise a problem that a constant level of drag, which is one of necessary functions as a knee bolster, cannot be maintained. Also, there is found another problem that, as shown in FIG. 14, in the latter half stage of the deformation thereof, the wall portion 7 of the stay 3a is opened outwardly so that the modulus of section thereof is lowered to thereby reduce the drag thereof.
Here, FIG. 9 is a graphical representation of relationships between the displacement of a knee bolster structure and a load to be applied thereto in the prior art and in the present invention. In particular, in the above-mentioned conventional knee bolster 1a, as shown by a dotted line C in FIG. 9, the load drops down extremely on the way and, as a reaction against to this extreme drop, there occurs an extreme peak in the load.
On the other hand, the above-cited known structures have their own characteristics but they also have the following problems: That is, in the knee protector structure disclosed in Japanese Patent Publication No. 2-175455 of Heisei, in spite of formation of the bending portion (13), the bending portion (13) is reinforced by the bent member (17), which is easy to raise a problem that the shock energy cannot be absorbed smoothly in a vehicle collision or the like. Also, there is found another problem that the flange (11) of the knee protector upper (3) can be opened outwardly in the latter half stage of the deformation thereof to thereby reduce the drag of the knee protector structure.
Also, in the knee protector disclosed in Japanese Patent Publication No.7-267026 of Heisei, provision of the bending lines (11a) and (18a) in the bracket (11) and upper bracket (18) can facilitate the absorption of the shock energy in a vehicle collision or the like; however, the object of this known structure is to prevent the vibration of the knee protector in a vehicle collision and, as a result of this, there is disclosed no device to maintain the drag of the knee protector at a constant level.
Further, in the knee protector disclosed in Japanese Patent Publication No. 7-81508 of Heisei, use of the substantially V-shaped first member (11) facilitates the deformation of the knee protector in a vehicle collision or the like to thereby absorb the shock energy and, at the same time, while the first member (11) is reinforced by the second member (12) properly, the second member (12) is fitted into the first member (11) to prevent interference with a crushing stroke, thereby facilitating the absorption of the shock energy. However, there is disclosed a rather insufficient device for stabilization of the drag of the knee protector and the whole structure is rather complicated and thus expensive in cost.
The present invention aims at eliminating the above-mentioned problems found in the conventional kneel bolster structures. Accordingly, it is an object of the invention to provide a simple and easy knee bolster structure which, while maintaining the drag thereof at a constant level, can absorb the shock energy to thereby buffer the shock applied from the knee portion of the occupant to the thigh portion thereof.